The Massachusetts Bay Transportation Authority (MBTA) Fiscal and Management Control Board (FMCB) voted May 7 to award a nearly $7 million contract to Hardesty & Hanover, LLC to design a replacement for the drawbridge above the Saugus River.

The project will fully replace the existing drawbridge that Newburyport/Rockport Line trains travel over, MBTA said. The existing bridge has been in service for more than a century, and the structure's condition is deteriorating despite repairs made throughout the years.

Progressing to the final design is intended to prevent additional costly repairs and potential service interruptions, MBTA said. The proposed bridge will stretch 530 feet in length and carry two railroad tracks above the Saugus River.

The draw span will be a rolling lift "Scherzer-style" bascule span, and the approach spans will be through-girder spans with reinforced concrete ballasted decks.

MBTA added that the useful life of the replacement structure is expected to be 75 years.

The new alignment and profile of the replacement bridge will be offline from the existing drawbridge, which MBTA said should ensure minimal impact to commuter rail service during the construction period and enable construction of the new rolling lift bascule span.

The rolling lift-style bascule is described as the economical choice for a movable span when construction is unaffected by the existing bridge or rail operations. This type of movable bridge is the preferred type for a small to medium span rail bridge.

Officials expect that the project will be advertised for construction in the fall of 2020 and that construction will be carried out throughout a three-year period.